Variable friction knee unit with an improved swing phase control of artificial legs

ABSTRACT

A variable friction knee unit that applies independent braking forces at different times to the swing phase of an artificial leg during walking which simulates the actions and efficiencies of the quadriceps and hamstring muscles of the thigh. Two braking modes are applied with an additional continuous braking mode. One operates at each end of swing phase. The second brake is applied a few degrees after the first brake and superimposed over the first brake. Both brakes are applied at each end of the swing phase of the walking cycle. In addition to being operative at the terminus of the swing, the two brakes are engaged at different times and are superimposed over the application of continuous friction so that the deceleration is a stepping function thereby simulating the function of the quadriceps and hamstring muscles of the thigh. The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

United StatesPatent Asbelle'et al.

[ July 4,1972

[54] VARIABLE FRICTION KNEE UNIT WITH AN IMPROVED SWING PHASE CONTROL OFARTIFICIAL LEGS [72] Inventors: Charles C. Asbelle, Oakland; Michael F.Arrigo, Berkeley; Kenneth E. Hunting, Hayward; Gene R. Helmuth, CastroValley, all of Calif.

[73] Assignee: The United States of America as represented by theSecretary of the Navy Barghausen ....3/28 Oliver ....3/26

I l i i x l Primary Examiner-Richard A. Gaudet Assistant Examiner-RonaldI... Frinks Attorney-R. S. Sciascia and Charles D. B. Curry [57]ABSTRACT A variable friction knee unit that applies independent brakingforces at different times to the swing phase of an artificial leg duringwalking which simulates the actions and efficiencies of the quadricepsand hamstring muscles of the thigh. Two braking modes are applied withan additional continuous braking mode. One operates at each end of swingphase. The second brake is applied a few degrees after the first brakeand superimposed over the first brake. Both brakes are applied at eachend of the swing phase of the walking cycle. In addition to beingoperative at the terminus of the swing, the two brakes are engaged atdifferent times and are superimposed over'the application of continuousfriction so that the deceleration is a stepping function therebysimulating the function of the quadriceps and hamstring muscles of thethigh.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

10 Claims, 8 Drawing Figures PATENTEDJUL 4|972 3,673,613

sum 1 or 4 2 47 i i i H I I E l 1 I l 55 I3 INVENTORS CHA P'A'TENTEDJuL4:972 3,673,613

sum 20F 4 VIIIIIIIII r INVENTORS 3 CHARLES C. ASB LE Ml AEL F. ARR KE THE. N G

GENE R. HE U H TORN Y BACKGROUND OF INVENTION 1 Field of the InventionThe present invention relates generally to a variable friction knee unitfor swing phase control in artificial legs and more particularly to aunit that applies two separate braking forces at different times to theswing phase of an artificial leg during walking, to simulate the naturalaction of the muscles of the thigh.

2. Description of the Prior Art The prior prosthetic limbs employed theuse of elastic bands, leather straps, wooden springs, andcontinuous-friction devices. And still other limbs employed hydrauliccylinders or spring-loaded brake materials to simulate thigh musclefunction. All of the aforementioned units were very unreliable andunstable in operation as well as sensitive to temperature changes,humidity, and overloads such as the amputee falling.

SUMMARY OF THE INVENTION Although there have been attempts at designingvariable friction knee brakes, the results have not been favorablyconsistent. Anearly model of the variable friction-brake used the dualbraking concept in a different manner with limited success. The maindevice consisted of split oilite bronze bearings contained in a rubberbushing at the knee block to receive the knee bolt. By tightening a nutto squeeze the rubber bushing to close the gap in bearings provided theeffective drag needed on the swing of the leg. The device consisted of aleft conventional brake and a right variable friction brake. Theconventional adjustable brake augmented the slight braking action of thetwo knee bearings. The right brake was also adjustable and oscillatedbetween two rubber stops to provide the variable friction function.Although superior to any prior system, it still did not simulate theactions and effeciencies of the quadriceps and hamstring muscles of thethigh. If a graph were made representing the function of these aforesaidmuscles during the swing phase operation, the friction application orenergy absorption during the curve extension phase would appear as anormal bell-shaped curve. The walking cycle of the leg consists of aflexion phase and extension phase. As pointed out above, the priordevice operated in a two-step operation Other objects, advantages andnovel features of the invention will become apparent from the followingdetailed description of the invention when considered in conjunctionwith the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric view of theknee portion of the artificial leg of the present invention, parts beingbroken away to illustrate the interior construction;

FIG. 2 is a transverse sectional view of the knee;

FIG. 3 is an exploded sectional view showing certain details ofconstruction of the unique dual offset brake system;

FIG. 3A is an exploded sectional view of one bearing structure of thedual bearing constant friction system;

FIG. 4A is a graphical representation of the normal walking cycle;

FIG. 4B is a graphical representation of the old two step device;

FIG. 4C is a graphical representation of the multiple step functiondevice; and

FIG. 5 is a side view of the knee to show certain details ofconstruction.

DESCRIPTION OF THE PREFERRED EMBODIMENT In order to facilitateunderstanding of the unique system, which is considered the subject ofthe present invention, a description of the relevant parts of theartificial limb (in conjunction with the present invention) follows.Referring to FIG.

thereby generating a very flat curve. However, it has been I found byexperimentation that by using two friction brakes at both ends of theangular swing phase, arranged to operate only during the last stages,and by engaging one brake a few degrees ahead of the other brake in amultiple step function action we very closely approximate the swingphase function of the quadriceps and hamstring muscles during theextension phase as represented by the bell curve. It should be notedthat during the flexion phase a multiple step function action would notbe required because much less energy is required to decelerate the legduring the flexion phase.

STATEMENTS OF THE OBJECTS OF THE INVENTION tificial leg which will allowmaximum clearance above the knee-bolt, permitting use with extremelylong-above-knee amputation stumps as well as possible adaptation to mostsingle knee structures.

I wherein the artificial limb 11 comprises shin portion 13 pivotallysuspended from thigh portion 15 and having a foot (not shown) secured tothe lower end of the limb ll. Thigh portion 15 is hollow and alsoadapted for fitted attachment to the stump of an amputee in the standardmanner. Shin portion 13 is of hollow construction and of standardlight-weight material. This construction is well known in the prostheticlimb art. The shin portion 13 and thigh portion 15 may be covered withany well known cosmetic material.

Referring to FIGS. 1 and 2, the pivotal suspension of the shin portion13 of the limb 11 is provided by hinge straps l7 and 19 suspended fromthigh portion 15 and secured to the shin portion 13. The hollow kneetubular bolt 23 extends through a transverse bore 21 in the thighportion 15. Hinge straps l7 and 19 are rotatably attached at either endof tubular bolt 23. The pivotal hinge straps l7 and 19 located on shaft23 are attached and secured to the inner wall of shin portion I3 in astandard manner of attachment well known in the art. The bolt 23 issecured to thigh portion 15 by strap screw 25. The variable frictionbraking device of the present invention comprises a first frictioncontrol brake device 27 and a second friction control brake device 37, aknee stop bumper arm 47 and continuous friction bearings 49 and 49'located on either side of the first brake device 27 and second breakdevice 37, pivotally mounted on the knee bolt 23. The knee stop bumperarm 47 is located between first brake device 27 and second brake device37, all being pivotally mounted on knee bolt 23.

FIG. 3 is an exploded sectional view showing certain details ofconstruction of the unique dual oflset brake system of the presentinvention. Continuous friction is applied to knee bolt 23 by bearings 49and 49' which are functionally and structurally the same. Therefore, thefollowing discussion of bearing 49 is equally applicable to bearing 49.An exploded view of bearing 49 is illustrated in FIG. 3A as comprising asplit bronze oilite bearing 49a encased in a neoprene cylinder 49!:which in turn is encased in aluminum casing 49c. Bearings 49 and 49 aremachined to fit on the shaft of tubular knee bolt 23. Outer casing 49cis hexagonally shaped and is cemented in transverse bore 21 of thighportion 15. With tubular knee bolt 23 in position, an outer gland nut49d screws into bearing casing 490 to compress neoprene cylinder 49bwhich in turn causes bearing 49a to clamp about bolt 23, therebyapplying continuous friction in the same manner as bearing 49'. The dualcontinuous clamping or friction action of bearings 49 and 49' is used toapply the conventional brake friction which is applied to all rotationsof knee bolt 23 within transverse bore 21" of thigh portion 15. Thisarrangement allows adjustment for wear of the bearings. The bearingdevice described is standard and well known in the art.

Referring to FIGS. 1, 2, and 3 wherein between first and second brakemeans 27. and 37 is knee stop bumper arm 47 made of aluminum, or othersimilar material, projecting down from thigh portion and into theplastic shin 13. The knee stop bumper arm 47 is pivotally suspended fromthe knee bolt 23 and has a single adjusting screw 51a located near theknee bolt 23. It should be noted that the knee stop arm 47 is fittedwith two oblong rubber bumpers 53 and 55.

Referring to FIG. 5 wherein the upper bumper 53 contacts knee block 57and the lower bumper 55 will sequentially contact each of the inner rearsurface of hypersensitive stop 59 of shin.l3 and forward portion 13a ofshin 13. Upon flexing the knee past 90, knee stop arm 47 will contactforward portion 13a and upper bumper stop 53 will push against kneeblock 57' to allow for at least about 120 of knee flexion. Uponextending the knee 1] the knee stop arm 47 resumes its originalposition. Adjustment of the adjusting screw 51, shown in FIG. 2, on theknee stop arm 47, should be just enough to prevent the. knee stop 47from moving forward during the walking cycle and to prevent it frommaking noise.

Referring to FIG. 3, knee stop arm 47 is provided with a transversecircular opening 470 with slot 47b extending tangentially outwardtherefrom. A bronze sleeve 61 may be positioned within the opening toact as a bearing. The function of the knee stop 57 is to determine thelimit of the pivotal movement of the. shin l3 portion of the leg in theextension direction. The bumpers 53 and 55 may be made of short sectionsof neoprene cord stock of 60 durometer which are installed so that ascompression takes place it will minimize the tendency, as in priormodels, of wiping" the bumper off its cemented surface. Brakes 27 and 37of the present invention are radically different in both function andmaterials from previous braking systems. That is, two brake bands arenow employed for the variable deceleration function while two bearingsapply continuous friction.

Referring to FIGS. .1, 2, and 3 wherein placement of stops 31 and 41 arearranged for onebrake to be applied a few degrees before the otherwhereas rear bumper stops 29 and 39 are in line and apply frictionforces on the flexion stage of the walking phase. As a result, the totalbraking effect comes about in two stages in. the extension phase ratherthan the more abrupt single stage. The significance of this result canbe seen by reference to FIGS. 4A, 4B, 4C.

In FIG. 4A the area of the curve above the abscissa 1: represents theextension phase of the walking cycle whereas the area of the curve belowthe abscissa it represents the flexion phase of the walking cycle. Itshould be noted that curves shown in FIGS. 4B and 4C show only theextension phase of the walking cycle since both the old and new devicesfunction in a similar mannerduring the flexion phase. Referring to FIG.4A wherein the area between the horizontal lines a represents theapplication of continuous braking friction, the area crosshatched underthe curve represents the total energy absorbed during the extensionflexion phase of the normal walking cycle of a non-amputee. Stepfunction line b is superimposed over the extension phase curve in FIG.4A to show the simulated equivalent variable friction multiple brakingsystem. Referring to FIG. 48 wherein cross-hatched area c represents theapplication of continuous friction that is the summation of the firstbrake friction and bearing friction. The area d under the curverepresents the total energy absorbed during the extension phase. Stepfunction 2 represents the application of a second brake or brake 2.Referring to FIG. 4C wherein the crosshatcl'led area f represents theapplication of the continuous bearing friction,.area 3 represents the.total energy absorbed during the extension phase. Step function Itrepresents the sequential application of brake l and brake 2. FIG. 4Ashows that more energy is required on the extension phase to deceleratethe extension swing of the leg than on the flexion phase. Therefore, wecan see that multiple step by step application of friction forces duringthe extension phase rather than continuous braking, plus a superimposedvariable friction brake application to the continuous braking, will moreclosely approximate the nonnal walking curve as shown in FIG. 4A.Referring to FIG. 413 wherein the first brake acts in conjunction withthe bearings and the second brake device is applied as a single stepfunction thereby creating a relatively flat extension phase cycle; FIG.4B shows that there is a great deal of variance from the ideal extensionphase walking and swing phase cycle shown in FIG. 4A. Referring to FIG.4C wherein the improved device with its step bystep friction applicationmore nearly simulates the normal walking cycle shown in FIG. 4A; it hasbeen found by experimentation that using continuous friction of thebearings, plus a step by step application of variable friction,approximates more closely the normal walking cycle and thereby simulatesthe action of the hamstrings and quadriceps muscles of the thigh. Infinal analysis, by comparing the normal swing phase cycle (shown in FIG.4A) with the mechanical simulation systems (shown in FIGS. 48 and 4C) itcan be readily observed that FIG. 4C more nearly simulates the normalextension phase cycle curve of the non-amputee, as shown in FIG. 4A.

Referring to FIG. 3 wherein the first and second friction brake meanscomprises two variable friction brakes 27 and 37 disposed upon bolt 23on each side of knee stop arm 47 and between adjustable bearings 49 and49; thevvariable friction brakes 27 and 37 apply their forcessuperimposed over the constant friction of the knee bearings 49 and 49'.Two brake bands '33 and 43 are made of automobile brake band materialrather than the standard leather brake material. While the singleoriginal leather limb brake presented a friction surface of about 0.79square inches, the new pair of brakes now encircling the surface of bolt23 present a total friction surface of about 3.76 square inches, anincrease of 475 percent.

Referring to FIGS. 2 and 5, when the shin 13 is extended from a flexedposition, bolt 23 and the knee stop arm 47, which is secured infrictional engagement therewith, the lower bumper 55 of knee stop arm 47will remain in position with its lower extremity abutting the posterioror hypersensitive stop 59 of the shin portion 13 of limb 11. As shinportion 13 is extended, the upper bumper 53, mounted on the farside ofthe knee stop arm 47, approaches stop 57 of the thigh 15. This preventsfurther pivotal movement of the shin portion 13 and provides a positiveextension stop.

As shin 13 is flexed rearwardly, the arm 47 moves therewith until theupper bumper 53 thereof on its rear side engages stop portion 57' of thethigh 15. This limits the amount of flexion. However, since the arm 47is secured to the shaft 23 for rotation therewith, as a consequence ofthe frictional pressure of the sleeve 61, further flexion of the shin 13is possible. This allows an amputee with along leg stump to bend shin 13of his leg past the right angle position with respect to the thigh.

Dual friction variable brake system: Referring to FIG. 2 wherein thebearings 49 and 49 provide the continuous application of friction forcesto the knee bolt 23; the second braking mode is superimposed over thefirst braking mode and both are applied to each end of the swing phaseof the walking cycle while the bearings are applying continuousfriction. Referring to FIG. 3 wherein the first variable frictionbrake27 comprises a rear horizontal bumper 27a, a vertical front bumper 27band adjusting screw 35; the rear bumper stop 29 engages with rearhorizontal stop 27a and front bumper stop 31 engages with front verticalstop 27b. Second variable friction brake 37 comprises a rear horizontalbumper 37a, a front vertical bumper 37b, and adjusting screw 45. Therear bumper 37a engages with rear bumper stop 39 and front bumper 37bengages with front bumper stop 41. Front bumperstops 31 and 41 areoffset in the horizontal plane from each other by about one-eighth inchso that the first brake 27 will apply a friction force about 5 in arebefore the application of friction forces of the second brake 37 duringthe extension phase.

That is, bumper stop 31 is about one-eighth inch ahead of bumper stop 41in the horizontal plane. Bumper stops 29 and 39 are not offset from eachother so that during the flexion phase of the walking cycle both brakesare applied at the same time. The first brake 27 has a builtin lag sothat the first brake 27 is not applied immediately upon rotation but isapplied a few degrees of are after application of continuous bearingfriction. This creates a step by step application of friction forces sothat the swing phase deceleration will more closely approximate thenormal swing phase cycle curve, thereby simulating the movement of thehamstring and quadriceps of the thigh.

What is claimed is:

l. A variable friction knee unit for an artificial limb including athigh portion pivotally attached to a shin portion and a swing phasecycle control located in said thigh portion to control the flexion phaseand extension phase of said swing phase said control comprising:

a. first variable friction means;

b. second variable friction means;

c. continuous friction means;

d. friction actuation means to intermittently actuate said first meansand said second means;

e. means for pivotally mounting said first means, said second means, andsaid continuous means;

f. said first means and said second means being operatively connected tosaid mounting means .whereby said first means and said second meanS areindependently actuated by said actuation means; and

g. stop means to limit the angular displacement of said shin during saidflexion phase and said extension phase.

2. The device recited in claim 1 wherein said actuation means comprises:

a. first actuation means;

b. second actuation means;

c. third actuation means;

d. fourth actuation means;

c. said first actuation means and said third actuation meansindependently and sequentially controlling the application of frictionby each of said first means and said second means during said extensionphase;

f. said second actuation means and said fourth actuation meansconcurrently controlling the application of friction by said first meansand said second means during said flexion phase.

3. The device recited in claim 2 wherein said first actuation means isstructurally offset from said third actuation means whereby said secondfriction means is actuated subsequent to said first friction meanswherein said second actuation means and said fourth activation means arein structural alignment whereby said second friction means and saidfirst friction means are activated simultaneously to apply friction.

4. The device recited in claim 3 wherein said first, second, third, andfourth actuation means are bumper stops wherein said first variablefriction means and said second variable friction means are variablefriction brakes, said brakes including brake linings.

'5. The device recited in claim 4 wherein said first brake and saidsecond brake each comprises:

a. horizontal rear bumper;

b. vertical front bumper;

c. said vertical bumper of said first brake being in intermittentoperative contact with said first bumper stop;

d. said horizontal bumper of said first brake being in intermittentoperative contact with said second bumper stop; e. said vertical bumperof said second brake being in intermittent operative contact with saidthird bumper stop; and 1 f. said horizontal bumper of said second brakebeing in intermittent operative contact with said fourth bumper stop.

6. The device recited in claim 5 wherein said first bumper stop isaligned in the horizontal plane ahead of said third bumper stop so thatsaid vertical bumper of said first brake contacts said first bumper stopa few degrees in are before said vertical bumper of said secondbrake'contacts said third bumper stop, whereby said second brake isactivated subsequent said first brake thereby causing a two-stagevariable friction braking action.

7. The device recited in claim 6 further includes a continuous frictionbraking means being superimposed over the variable application offriction of said first brake and said second brake.

8. The device recited in claim 7 wherein said continuous friction meansis a bearing device, said bearing comprising a. first bearing;

b. second bearing;

0. said first bearing and said second bearing applying continuousbearing friction precedent to the friction braking action of said firstbrake and said second brake.

9. The device recited in claim 8 wherein said first brake and saidsecond brake are positioned on either side of a flexion extensionlirniting stop and interjacent said first bearing and second bearing,said first brake, said second brake, said limiting stop, said firstbearing, said second bearing all pivotally mounted on a circular bolt,said bolt extending through the thigh portion of an artificial limb toform an axis joint to con trol the flexion and extermion of a shinportion of an artificial limb. I

10. The device recited in claim 9 wherein said first brake and saidsecond brake include a brake lining made of automobile brake bandmaterial, said lining operatively circumambient said bolt.

I i t t

1. A variable friction knee unit for an artificial limb including athigh portion pivotally attached to a shin portion and a swing phasecycle control located in said thigh portion to control the flexion phaseand extension phase of said swing phase said control comprising: a.first variable friction means; b. second variable friction means; c.continuous friction means; d. friction actuation means to intermittentlyactuate said first means and said second means; e. means for pivotallymounting said first means, said second means, and said continuous means;f. said first means and said second means being operatively connected tosaid mounting means whereby said first means and said second mEanS areindependently actuated by said actuation means; and g. stop means tolimit the angular displacement of said shin during said flexion phaseand said extension phase.
 2. The device recited in claim 1 wherein saidactuation means comprises: a. first actuation means; b. second actuationmeans; c. third actuation means; d. fourth actuation means; e. saidfirst actuation means and said third actuation means independently andsequentially controlling the application of friction by each of saidfirst means and said second means during said extension phase; f. saidsecond actuation means and said fourth actuation means concurrentlycontrolling the application of friction by said first means and saidsecond means during said flexion phase.
 3. The device recited in claim 2wherein said first actuation means is structurally offset from saidthird actuation means whereby said second friction means is actuatedsubsequent to said first friction means wherein said second actuationmeans and said fourth activation means are in structural alignmentwhereby said second friction means and said first friction means areactivated simultaneously to apply friction.
 4. The device recited inclaim 3 wherein said first, second, third, and fourth actuation meansare bumper stops wherein said first variable friction means and saidsecond variable friction means are variable friction brakes, said brakesincluding brake linings.
 5. The device recited in claim 4 wherein saidfirst brake and said second brake each comprises: a. horizontal rearbumper; b. vertical front bumper; c. said vertical bumper of said firstbrake being in intermittent operative contact with said first bumperstop; d. said horizontal bumper of said first brake being inintermittent operative contact with said second bumper stop; e. saidvertical bumper of said second brake being in intermittent operativecontact with said third bumper stop; and f. said horizontal bumper ofsaid second brake being in intermittent operative contact with saidfourth bumper stop.
 6. The device recited in claim 5 wherein said firstbumper stop is aligned in the horizontal plane ahead of said thirdbumper stop so that said vertical bumper of said first brake contactssaid first bumper stop a few degrees in arc before said vertical bumperof said second brake contacts said third bumper stop, whereby saidsecond brake is activated subsequent said first brake thereby causing atwo-stage variable friction braking action.
 7. The device recited inclaim 6 further includes a continuous friction braking means beingsuperimposed over the variable application of friction of said firstbrake and said second brake.
 8. The device recited in claim 7 whereinsaid continuous friction means is a bearing device, said bearingcomprising a. first bearing; b. second bearing; c. said first bearingand said second bearing applying continuous bearing friction precedentto the friction braking action of said first brake and said secondbrake.
 9. The device recited in claim 8 wherein said first brake andsaid second brake are positioned on either side of a flexion extensionlimiting stop and interjacent said first bearing and second bearing,said first brake, said second brake, said limiting stop, said firstbearing, said second bearing all pivotally mounted on a circular bolt,said bolt extending through the thigh portion of an artificial limb toform an axis joint to control the flexion and extension of a shinportion of an artificial limb.
 10. The device recited in claim 9 whereinsaid first brake and said second brake include a brake lining made ofautomobile brake band material, said lining operatively circumambientsaid bolt.